Fuse



July 19, 1932. .1. D. ROBERTS ET AL FUSE Filed March 22, 1929 Patented July 19, 1932 UNITED STATES PATENT orrica JOSEPH 1). ROBERTS, 0F SPRINGFIELD, AND GYBIL H. THOMAS, OF CHICAGO, ILLINOIS; SAID ROBERTS. ASSIGNOR TO SAID THOMAS ruse , Application filed March 22, 1929. Serial No. 349,048.

Our invention relates in general to electrical switching apparatus and has more particular reference to an improved circuit protector of the fusible link type for rupturing a circuit when predetermined overload conditions occur.

Fusible links of this general nature cornprise strips of electrical conducting material of suitable cross sectional area mounted in a suitable holder and arranged in the circuit so that when overload conditions occur, the link will be heated to the melting point and fall out of the circuit.

WVhile it is usually desirable to rupture the circuit quickly when continuous overload conditions prevail, it is not desirable to have an extremely sensitive fuse which will blow upon the instantaneous overloads or surges, which occur intermittently in electrical transmission and distribution lines. For this reason the cross section of links are made of sufiicient area so that the fuse link will not heat to fusing temperature and be blown out upon'instantaneous overload, but will carry the overload for an appreciable time. One result of this is that standard fuses will carry light overloads for extended periods without becoming heated to the fusion polnt.

Aluminum wire, for instance, which is frequently employed as a fuse link, fuses at approximately 1200 F. (barely visible red heat) and of course an aluminum fuse Wlll carry an overload current which is not sufficientto heat the wire to 1200 F., continuously at this destructive temperature.

An important object of our present invention is to provide a fuse link, which is relatively insensitive to instantaneous overloads but which will operate rapidly and positively to rupture a circuit even when the overloading of the circuit is slight, provided it be continuous.

Another important object of our invention is to provide a fuse link which will rupture instantaneously when a given overload has been carried for a predetermined interval.

Still another important object of our invention is to provide a fuse link which blows explosively whereby the fuse link when used in an expulsion fuse maycompletely remove itself from its holder.

Still another important object is to provide a fuse link wherein means is provided to speed the operation of the fuse when predetermined overload conditions prevail whereby preciaccomplished. a

Still another object is to provide a fuse link wherein the inertia or lag of the fuse against blowing is maintained for instantaneous overloads or surges, but is off-set when the link is subjected to continuous overloads.

Numerous other important objects and advantages of the invention will be apparent as it is more fully understood from the following description which taken in connection with. the accompanying drawing, discloses a preferred embodiment.

Referring to the drawing:

Figure l is a longitudinal section taken thrpugh a fuse link embodying our invention; anc

Figures 2, 3 and 4 are longitudinal sections taken substantially and respectively along the lines 22, 8-3 and 4-4 in Figure 1.

To illustrate our invention we have shown on the drawing a fuse link comprising a current conducting fusible member 11 having a reduced portion 13. This fusible member may be conveniently formed by braiding together two wires 15 of a suitable fuse material, a section of one wire being removed at a point where the reduced section is desired. Such a fuse member may be inserted between the terminals of a suitable fuse support and connected in an electric circuit as a protection against overloads. When overload conditions prevail in the circuit, the electrical resistance at the reduced portion of the fusible member will cause heat to be generated at such reduced portion under normal circumstances and in fuses of the ordinary construction heretofore provided, the fuse will maintain the circuit until sufficient heat is generated to fuse the member at its reduced portions. If the overload never becomes sufiiciently great to generate sufficient sion control of the electric circuitsmay be heat to melt the fuse link, the circuit will be maintained indefinitely.

In order to provide a fuse link highly sensitive to continued overloading, we surround the reduced section 13 of the fusible link 11 with fast-burnng material 23, which will be ignited by the heat generated in the fuse link at a temperature substantially lower than the fusing point of the material of which the link is composed. Various quick burning substances may be employed for this purpose, but we prefer to use ordinary commercial flash light powder, which ignites at a temperature of 650 F.

r The combustible material 23 burns instantaneously with explosive violence and forms an additional source of heat which will im' mediately burn up the fuse link and thus rupture positively and instantaneously the circuit in which it is arranged.

Flash light powder and certain other available explosives are good conductors of electricity for which reason it is necessary to insulate the fusible member 11 from the fast burning material 23. For this purpose we provide the member 11 with a coating or film 17 of a suitable non-conducting varnish and extend this film substantially beyond the reduced section of the fusible member 11, as illustrated by the dotted lines 19 in Figure l, which approximately define the preferred limits between which the film of varnish 17 is applied. To retain the combustible material in place around the reduced section of the fusible member 11, we provide a housing or enclosing capsule of non-conducting combustible material.

In the illustrated embodiment this capsule comprises a celluloid tube 21, which encircles the reduced section 18 of the fusible member 11, and encloses the fast-burning material 23. The ends of the cylinder are closed by discs or wads of resilient material, preferably asbestos, which are packed into the ends of the tube 21 to keep the fast burning material in place. The ends of the tube above these discs are closed against the entrance of moisture. This may be accomplished by applying acetone to the ends of the tube and then clamping the ends upon the fusible member 11. Acetone, being a solvent for celluloid, softens the ends of the tube and permits them to be clamped against the member 11. Upon the evaporation of the acetone, the clamped ends of the tube form a moisture proof connection through which the ends of the fusible member 11 extend.

We prefer however to seal the ends of the tube by poring liquid celluloid, that is to say, a solution of celluloid in acetone into the open ends of the tube above the washer 25 and around the protruding ends of the fusible member 11, as clearly illustrated in Figure 1 of the drawing.

Celluloid is particularly adapted for use in forming an enclosing capsule for the fastburning material 23, for the reason that it is non-conducting, and is also highly inflammable, so that when the fuse is blown, practically all the materials which form the fuse link, will be completely burned and consumed.

When the fuse link of our invention is arranged in a circuit and subjected to overload conditions, the reduced section 13 of the fusible member 11 will be heated. By suitably controlling the area of this reduced section, the fuse may be arranged to produce sufiicient heat to ignite the combustible material 23 when predetermined overload conditions prevail. At this critical point there will be no time lag in the operation of the fuse but the fuse will be exploded instantaneously.

The fuse link which we have described is of special advantage when used in fuses of the so called expulsion type for the reason that the explosion of the fast-burning material 23, assists in blowing the fuse element entirely out of the fuse link holder, so that when the link is to be replaced, no time need be wasted in removing partial expelled portions of the fuse link.

It is thought that the invention and numerous of its attendant advantages will be understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the various parts without departing from the spirit or scope of our in vention or sacrificing any of its attendant advantages, the form hereinbefore described being of a preferred embodiment.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. In a fuse, a current conducting fusible link having a reduced section, a film of insulating varnish coating said reduced section,

a quantity of flash light powder arranged around said reduced portion and means including a celluloid housing enclosing said flash light powder to secure it about the restricted portion.

2. In a fuse, the combination of a currentconducting member, a tube of celluloid surrounding said member with the ends of the latter projecting therefrom, a quantity of quick-burningmaterial disposed within the tube and encircling the member, means disposed between the ends of the tube and said quick-burning material for holding the latter tightly in place, said means having apertures through which the conducting member projects, and means forming a moistureproof connection between the ends of the eel.- luloid tubing and the projecting ends of the conducting member.

3. In a fuse, the combination of a housing of celluloid, a conducting member passing through said housing with its ends projecting therefrom, a quantity of quick-burning material disposed in the housing and about the conducting member, and means forming a moisture-proof connection between the ends of the housing and the projecting ends of the conducting member.

4. In a fuse, the combination of a housing of non-conducting highly inflammable material, a conducting member having its ends projecting from the opposite ends of the housing, a quantity of quick-burning material in said housing about the intermediate portion of said conducting member, and means for closing the ends of said housing and for providing a moisture-proof connection between it, and the ends of the conducting member.

5. In a fuse, the combination of a celluloid housing, a conducting member having its ends projecting therethrough, a quantity of quick-burning material in said housin and around the conducting member, said celIuloid housing being sealed to the conducting member to exclude moisture.

6. In a fuse, the combination of a celluloid housing, a conducting member passing therethrough with its ends projecting from the end of the housing, a quantity of quick-burning material about the conducting member in said celluloid housing, the ends of said tube being closed about the ends of the conducting member by a solidified solution of celluloid in acetone, whereby to exclude moisture.

7. A fuse comprising a tubular housing of highly inflammable non-conducting material which is soluble in acetone, a conducting member having its ends projecting from the ends of the tube, a quantity of quick-burning material in said tube about the conducting member, and means for sealing the ends of said tube above the non-conducting member,

said means being constructed and arranged to exclude moisture.

8. A fuse comprising a housing of combustible, non-conducting material, a conductor passing through said housing with its ends projecting therefrom, a quantity of quick-burning material in said housing and about said conductor, and means moldable to the projecting ends of the conductor and to the housing, for sealing the ends of the housing and forming a moisture-proof connection therefor.

9. A fuse comprising an elongated tubular housing of highly inflammable non-conducting material, a fuse passing therethrough having a central reduced ortion and having portions projecting from t e ends of the housing, said central portion of the fuse having a coating of non-conducting material, a quantity of quick-burning material disposed in the intermediate portion of said housing about said reduced portion of the fuse, there being partition members of resilient material between each end of the housing and said quick-burning material, said partition members having openings through which the ends of the fuses pass, said housing being closed by a quantity of moldable material forming a sealed connection between the end pails of said housing and the ends of the use.

10. A fuse comprising a tubular housing of highly inflammable non-conducting material, a conducting member having its ends projecting from the ends of the tube, a quantity of quick-burning material in said tube about the conducting member, and means for sealing the ends of said tube above the nonconducting member, said means being constructed and arranged to exclude moisture.

In witness whereof, we have hereunto subscribed our names.

JOSEPH D. ROBERTS. OYRIL H. THOMAS. 

